In order to dampen irregularities in the drive leading to the subsidiary drives, prior art driving discs are commonly provided with spring and damping elements made of elastomer products which combine a spring and damping effect in one component (DE 197 49 421 C2).
Elastomer, when used as a material for spring and damping elements, comprises a number of disadvantages. The stiffness and thus the natural frequency of the spring and damping element greatly depends on the ambient temperature, which adversely affects the damping effect when the ambient temperature changes. Apart from external influences, the ambient temperature changes even as a result of the internal damping over time.
Elastomer is also susceptible to environmental influences; more particularly, it can be attacked by aggressive fluids or oils as well as gases which occur in internal combustion engines.
The damping characteristics of an elastomer are primarily dependent on the properties of the elastomer, which properties can be varied to a limited extent only. In addition, the spring and damping elements made of elastomer require a relatively large installation space.
In EP 0 782 674 B1, a driving disc is provided in the form of a crankshaft decoupling device wherein a spring disc is fixed to a mounted hub and a belt pulley. In addition, curved helical springs are arranged circumferentially extending and mounted without a pretension, and which extend in the same circumferential direction between the driving disc and the belt pulley. The driving disc is combined with a slip coupling switched to operate in a specific direction.
DE 602 00 178 T2 provides a belt pulley unit, for an internal combustion engine wherein the coupling means are provided in the form of one or two metallic spiral springs between a hub and an annular element for the belt seat. The coupling means exhibits a different behavior as a function of the tendency of the hub to rotate faster or more slowly than the annular element. The coupling means provide a flexible coupling with an increasing stiffness as a consequence of an increasing tendency of the hub to rotate faster than the annular element. In addition, the coupling means has a tendency to disconnect the hub from the annular element with an increasing tendency of the hub to rotate more slowly than the annular element. In the latter case, the spiral springs are completely load-relieved, so that noise develops at their points of support.